U.S. patent number 8,747,472 [Application Number 12/541,785] was granted by the patent office on 2014-06-10 for spinal therapy device with fixated distraction distance.
This patent grant is currently assigned to Baxano Surgical, Inc.. The grantee listed for this patent is Stephen D. Ainsworth, Leighton J. LaPierre. Invention is credited to Stephen D. Ainsworth, Leighton J. LaPierre.
United States Patent |
8,747,472 |
Ainsworth , et al. |
June 10, 2014 |
Spinal therapy device with fixated distraction distance
Abstract
Assemblies for implantation across one or more spinal motion
segments to allow for control of the distance between bone anchors.
Control of distance between bone anchors may be provided by one
inter-anchor element pushing the pair of bone anchors apart and a
second inter-anchor element pulling the pair of bone anchors
together. Control of distance between bone anchors may be provided
through use of dissimilar thread pitch. Compression of
intervertebral disc space through controlled movement of a pair of
anchored bone anchors towards one another.
Inventors: |
Ainsworth; Stephen D.
(Wilmington, NC), LaPierre; Leighton J. (Wilmington,
NC) |
Applicant: |
Name |
City |
State |
Country |
Type |
Ainsworth; Stephen D.
LaPierre; Leighton J. |
Wilmington
Wilmington |
NC
NC |
US
US |
|
|
Assignee: |
Baxano Surgical, Inc. (Raleigh,
NC)
|
Family
ID: |
43586447 |
Appl.
No.: |
12/541,785 |
Filed: |
August 14, 2009 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110040329 A1 |
Feb 17, 2011 |
|
Current U.S.
Class: |
623/17.11;
606/105; 606/326; 606/328; 606/320 |
Current CPC
Class: |
A61B
17/70 (20130101); A61B 17/7014 (20130101); A61F
2/4611 (20130101); A61F 2/4601 (20130101) |
Current International
Class: |
A61F
2/44 (20060101) |
Field of
Search: |
;623/17.11-17.16
;606/90,105,246,247,258,259,261,300,320,328,301-317,318,319,326,327,251,63,68
;411/384 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Rathke/Schlegel--surgery of the spine --Atlas of Orthopedic
Operations, vol. 1,--1979 --pp. 222-224. cited by applicant .
International Search Report and Written Opinion From Corresponding
PCT Application No. PCT/US2010/045135, Oct. 6, 2010 (15 pgs). cited
by applicant.
|
Primary Examiner: Merene; Jan Christopher
Assistant Examiner: Mahmud; Atiya
Attorney, Agent or Firm: Flynn; Kevin E. Flynn IP Law
Claims
What is claimed is:
1. An assembly for implantation across two spinal vertebrae
comprising: an externally threaded distal anchor for engagement
with a distal vertebra; an externally threaded proximal anchor for
engagement with a proximal vertebra; a spanning component that is
threadedly engaged with the proximal anchor and extends into an
interior of the distal anchor, wherein the spanning component may
be rotated to set a minimum distance between a distal end of the
proximal anchor and a proximal end of the distal anchor; and a
compression inducing element adapted to: extend into an open
interior of the spanning component; engage a shoulder within an
interior of the proximal anchor, the shoulder facing a proximal end
of the proximal anchor; engage a threaded bore within an interior
of the distal anchor; and receive rotational input at a driver
engagement section at a proximal end of the compression inducing
element accessible via a proximal end of the proximal anchor such
that a driver engaged with the driver engagement section of the
compression inducing element has a capacity to reduce a distance
between the distal anchor and the proximal anchor by pulling the
distal anchor towards the proximal anchor, and wherein the shoulder
within the interior of the proximal anchor is part of a component
threadedly engaged to the interior of the proximal anchor.
2. The assembly of claim 1 wherein the spanning component imposes
the minimum distance between the distal anchor and the proximal
anchor, the minimum distance selected from a range of different
possible minimum distances enabled by a capacity of the spanning
component to move via threaded engagement relative to a threaded
portion of the interior of the proximal anchor.
3. The assembly of claim 2 where the range of different possible
minimum distances is broad enough to allow imposition of a
hyper-distraction distance between the distal anchor and the
proximal anchor to allow delivery of material into a
hyper-distracted space between the distal vertebra and the proximal
vertebra before using the compression inducing element to reduce
the distance between the distal anchor and the proximal anchor and
thus reduce the distance between the distal vertebra and the
proximal vertebra.
4. The assembly of claim 2 wherein the compression inducing element
limits the distance between the distal anchor and the proximal
anchor to not exceed the minimum distance imposed by the spanning
component.
5. The assembly of claim 1 wherein the distal anchor is adapted to
engage two adjacent vertebrae.
6. The assembly of claim 5 where the distal anchor is adapted to
distract an intervertebral disc space between the two adjacent
vertebrae through a use of dissimilar thread pitch.
7. The assembly of claim 1 wherein a portion of the spanning
component extending into the interior of the distal anchor is
fluted to reduce contact area between the spanning component and
the distal anchor.
8. The assembly of claim 1 wherein a portion of the spanning
component extending into the interior of the distal anchor is
adapted to reduce surface contact between the portion of the
spanning component and the interior of the distal anchor.
9. The assembly of claim 1 wherein the spanning component has at
least one lateral port in fluid communication with a proximal end
of the spanning component so that the spanning component may be
used as a conduit to deliver material between the distal vertebra
and the proximal vertebra.
10. The assembly of claim 1 wherein: the spanning component has a
spanning component driver engagement section at a distal end; the
distal anchor has a distal anchor driver engagement section at a
proximal end; and the spanning component driver engagement section
has a relationship with the distal anchor driver engagement section
such that one driver tip could be inserted from the proximal end to
simultaneously engage both the spanning component driver engagement
section and the distal anchor driver engagement section to allow
both to be torqued, and wherein another driver tip could be used
that would be capable to engage the spanning component driver
engagement section but not the distal anchor driver engagement
section such that the spanning component may be rotated without
driving the distal anchor.
11. The assembly of claim 1 wherein the proximal vertebra is a
portion of a sacrum.
12. The assembly of claim 1 wherein a proximal end of the proximal
anchor is adapted to engage a counter-torque tube.
13. An assembly for implantation across two spinal vertebrae
comprising: an externally threaded distal anchor for engagement
with a distal vertebra; an externally threaded proximal anchor for
engagement with a proximal vertebra; a spanning component that is
threadedly engaged with the proximal anchor and extends into an
interior of the distal anchor, the spanning component may be
rotated to set a minimum distance between a distal end of the
proximal anchor and a proximal end of the distal anchor; and a
compression inducing element adapted to: extend into an open
interior of the spanning component; engage a shoulder within an
interior of the proximal anchor, the shoulder facing a proximal end
of the proximal anchor; and threadedly engage an interior of the
distal anchor such that rotation of the compression inducing
element while threadedly engaged with the interior of the distal
anchor has a capacity to reduce a distance between the distal
anchor and the proximal anchor, and wherein the shoulder within the
interior of the proximal anchor is part of a component threadedly
engaged to the interior of the proximal anchor.
14. The assembly of claim 13 wherein the spanning component imposes
the minimum distance between the distal anchor and the proximal
anchor, the minimum distance selected from a range of different
possible minimum distances enabled by a capacity of the spanning
component to move via threaded engagement relative to a threaded
portion of the interior of the proximal anchor.
15. The assembly of claim 14 where the range of different possible
minimum distances is broad enough to allow imposition of a
hyper-distraction distance between the distal anchor and the
proximal anchor to allow delivery of material into a
hyper-distracted space between the distal vertebra and the proximal
vertebra before using the compression inducing element to reduce
the distance between the distal anchor and the proximal anchor and
thus reduce the distance between the distal vertebra and the
proximal vertebra.
16. The assembly of claim 14 wherein the compression inducing
element limits the distance between the distal anchor and the
proximal anchor to not exceed the minimum distance imposed by the
spanning component.
17. The assembly of claim 13 wherein the distal anchor is adapted
to engage two adjacent vertebrae.
18. The assembly of claim 17 where the distal anchor is adapted to
distract an intervertebral disc space between the two adjacent
vertebrae through a use of dissimilar thread pitch.
19. The assembly of claim 13 wherein a portion of the spanning
component extending into the interior of the distal anchor is
fluted to reduce contact area between the spanning component and
the distal anchor.
20. The assembly of claim 13 wherein a portion of the spanning
component extending into the interior of the distal anchor is
adapted to reduce surface contact between the portion of the
spanning component and the interior of the distal anchor.
21. The assembly of claim 13 wherein the spanning component has at
least one lateral port in fluid communication with a proximal end
of the spanning component so that the spanning component may be
used as a conduit to deliver material between the distal vertebra
and the proximal vertebra.
22. The assembly of claim 13 wherein: the spanning component has a
spanning component driver engagement section at a distal end; the
distal anchor has a distal anchor driver engagement section at a
proximal end; and the spanning component driver engagement section
has a relationship with the distal anchor driver engagement section
such that one driver tip could be inserted from the proximal end to
simultaneously engage both the spanning component driver engagement
section and the distal anchor driver engagement section to allow
both to be torqued, and wherein another driver tip could be used
that would be capable to engage the spanning component driver
engagement section but not the distal anchor driver engagement
section such that the spanning component may be rotated without
driving the distal anchor.
23. The assembly of claim 13 wherein the proximal vertebra is a
portion of a sacrum.
24. The assembly of claim 13 wherein a proximal end of the proximal
anchor is adapted to engage a counter-torque tube.
25. An assembly for insertion across an intervertebral space in a
spine via a trans-sacral access channel, the assembly comprising: a
distal anchor for threaded engagement with a more distal vertebral
body; a proximal anchor for threaded engagement with a more
proximal vertebral body separated from the more distal vertebral
body by an intervertebral disc space; a spanning component with an
external thread adapted to engage an internal thread within the
proximal anchor so that a distal end of the spanning component can
be selectively advanced beyond a distal end of the proximal anchor
to limit movement of the distal anchor towards the proximal anchor;
and a compression inducing element with a distal end that passes
through a bore in the spanning component and engages a threaded
bore in the distal anchor, the compression inducing element having
a distal facing shoulder which engages a proximal facing shoulder
within the proximal anchor so that rotation of the compression
inducing element draws the distal anchor towards the proximal
anchor to decrease distraction of the intervertebral space by
decreasing a distance between the distal anchor and the proximal
anchor until limited by the spanning component.
26. The assembly of claim 25 wherein the spanning component imposes
a minimum distance between the distal anchor and the proximal
anchor, the minimum distance selected from a range of different
possible minimum distances enabled by a capacity of the spanning
component to move via threaded engagement relative to a threaded
portion of an interior of the proximal anchor.
27. The assembly of claim 26 where the range of different possible
minimum distances is broad enough to allow imposition of a
hyper-distraction distance between the distal anchor and the
proximal anchor to allow delivery of material into a
hyper-distracted space between the distal vertebra and the proximal
vertebra before using the compression inducing element to reduce
the distance between the distal anchor and the proximal anchor and
thus reduce the distance between the distal vertebra and the
proximal vertebra.
28. The assembly of claim 26 wherein the compression inducing
element limits the distance between the distal anchor and the
proximal anchor to not exceed the minimum distance imposed by the
spanning component.
29. The assembly of claim 25 wherein the distal anchor is adapted
to engage two adjacent vertebrae.
30. The assembly of claim 29 where the distal anchor is adapted to
distract an intervertebral disc space between the two adjacent
vertebrae through a use of dissimilar thread pitch.
31. The assembly of claim 25 wherein a portion of the spanning
component extending into an interior of the distal anchor is fluted
to reduce contact area between the spanning component and the
distal anchor.
32. The assembly of claim 25 wherein a portion of the spanning
component extending into an interior of the distal anchor is
adapted to reduce surface contact between the portion of the
spanning component and an interior of the distal anchor.
33. The assembly of claim 25 wherein the spanning component has at
least one lateral port in fluid communication with a proximal end
of the spanning component so that the spanning component may be
used as a conduit to deliver material between the distal vertebra
and the proximal vertebra.
34. The assembly of claim 25 wherein: the spanning component has a
spanning component driver engagement section at a distal end; the
distal anchor has a distal anchor driver engagement section at a
proximal end; and the spanning component driver engagement section
has a relationship with the distal anchor driver engagement section
such that one driver tip could be inserted from the proximal end to
simultaneously engage both the spanning component driver engagement
section and the distal anchor driver engagement section to allow
both to be torqued, and wherein another driver tip could be used to
engage the spanning component driver engagement section but not the
distal anchor driver engagement section such that the spanning
component may be rotated without driving the distal anchor.
35. The assembly of claim 25 wherein the proximal vertebra is a
portion of a sacrum.
36. The assembly of claim 25 wherein a proximal end of the proximal
anchor is adapted to engage a counter-torque tube.
Description
BACKGROUND
1. Field of the Disclosure
The present disclosure relates generally to implantable device
assemblies, instrumentation systems, and methods for accessing and
treating multiple levels of the lumbar spine via a
minimally-invasive trans-sacral approach (as described in U.S. Pat.
No. 6,558,390 which is incorporated herein by reference). More
specifically, in one aspect of the disclosure, the present
disclosure generally relates to the imposition of a sequence of two
or more distractions on a set of two or more adjacent motion
segments as part of the provision of therapy to the spine. The
therapy may include an objective to stabilize a portion of the
spine and may further include using fusion as part of that
stabilization.
The distraction process involves setting a minimum distance between
a pair of bone anchors and then locking the bone anchors together
to prevent the bone anchors from moving beyond that minimum
distance between the bone anchors. One set of teachings within the
disclosure teaches a way to compress the distance between two
adjacent vertebrae by pulling the bone anchors in the two vertebrae
towards each other to provide control over the final distraction
distance between the vertebrae and to allow for the imposition of
compression of the material placed between the vertebrae.
2. Background Information and Related Art
The concept of providing therapy to adjacent motion segments
including fusion therapy is addressed in co-pending and commonly
assigned U.S. patent application Ser. No. 11/202,655 for Methods
and Apparatus for Provision of Therapy to Adjacent Motion Segments
published Mar. 16, 2006 as U.S. Pub. No. 2006/0058800 A1 and
incorporated by reference herein.
The individual motion segments within the spinal columns allow
movement within constrained limits and provide protection for the
spinal cord. A motion segment includes two adjacent vertebrae and
the disc between them. The discs are important to allow the spinal
column to be flexible and to bear the large forces that pass
through the spinal column as a person walks, bends, lifts, or
otherwise moves. Unfortunately, for a number of reasons referenced
in the '655 application, for some people one or more discs in the
spinal column will not operate as intended. The reasons for disc
problems range from a congenital defect, disease, injury, or
degeneration attributable to aging. Often when the discs are not
operating properly, the gap between adjacent vertebral bodies is
reduced and this reduction in distance causes additional problems
including pain.
A range of therapies have been developed to alleviate the pain
associated with disc problems. One class of solutions is to remove
the failed disc and then fuse the two adjacent vertebral bodies
together with a permanent but inflexible spacing, also referred to
as static stabilization. Fusing one section together ends the
ability to flex in that motion segment. However, as each motion
segment only contributes a small portion of the overall flexibility
of the spine, it can be a reasonable trade-off to give up the
flexibility of a motion segment in an effort to alleviate
significant back pain.
Fusion is one type of stabilization. Other forms of stabilization
may be used to alter the relative positions of components.
Generally, one of the first steps in trying to provide
stabilization therapy including fusion therapy is to move adjacent
vertebral bodies relative to one another (called distraction) to
compensate for the reduction of intervertebral space attributed to
the problems with the disc. Depending on the type of therapy that
is to be delivered, it may be useful to separate the adjacent
vertebral bodies by more than a normal amount of separation.
3. Vocabulary
It is useful to set forth some of the standard medical vocabulary
before getting into a more detailed discussion of the background of
the present invention. In the context of this discussion: anterior
refers to in front of the spinal column (ventral); and posterior
refers to behind the column (dorsal); cephalad means towards the
patient's head (sometimes "superior"); caudal (sometimes
"inferior") refers to the direction or location that is closer to
the feet.
As the present application contemplates accessing the various
vertebral bodies and intervertebral spaces through a preferred
approach that comes in from the sacrum and moves towards the head,
proximal and distal are defined in context of this approach.
Consequently, proximal is closer to the beginning of the channel
and the surgeon's hand outside the channel and thus towards the
sacrum of the patient. Distal is further from the beginning of the
channel and the surgeon and thus towards the head of the
patient.
While the general concept of distraction can be applied for moving
one item apart from another in any dimension, in the context of
this application and the claims that follow, distraction is
considered in the orientation of the axes of the spinal column so
that distraction increases the distance between two adjacent
vertebral bodies as measured in the direction of the
cephalad/caudal axis of the spine.
One of skill in the art will recognize that a separate process
known as subsidence may cause movement of the anchors and the
components attached to the anchor relative to the vertebral body
that holds the anchor. In some instances, the distance between
intervertebral bodies may move due to subsidence or analogous
process. From another viewpoint, the distraction between adjacent
vertebrae goes to zero when the fusion process connects the two
vertebrae together so there is no longer an intervertebral disc
space. Thus, when this application refers to fixation of the
distraction distance, all that can be controlled with certainty is
the distance between the relevant anchors.
The disclosure addresses the controlled movement of bone anchors to
either move them further apart from one another or move them closer
together. One of skill in the art will recognize that unless
otherwise specified explicitly, that motion of anchors will be
relative motion that is a mere statement that the anchors are
getting closer together or further apart. Thus if one anchor is
pulled towards another it means that the relative distance between
the two anchors is reduced. It does not mean that one anchor needs
to be stationary and one anchor needs to do all the moving or that
both anchors are moving relative to some external point of
reference. The specific allocation of which anchor is moving
relative to an external point of reference such as the operating
table may be influenced by other factors such as how the patient is
positioned and held on the operating table.
SUMMARY OF THE DISCLOSURE
Aspects of the teachings contained within this disclosure are
addressed in the claims submitted with this application upon
filing. Rather than adding redundant restatements of the contents
of each of the claims, these claims should be considered
incorporated by reference into this summary.
One set of teachings may be summarized by:
A method for controlling a distance between two bone anchors, the
method comprising: implanting a distal bone anchor in a distal
vertebral body; implanting a proximal bone anchor in a proximal
vertebral body, the proximal vertebral body adjacent to and
proximal to the distal vertebral body; threadedly engaging a first
inter-anchor element with an interior bore within the proximal bone
anchor and threadedly advancing the first inter-anchor element
distally within the proximal bone anchor to cause a distal portion
of the first inter-anchor element to push against the distal bone
anchor; inserting a threaded portion of a second inter-anchor
element through a channel within the first inter-anchor element and
engaging a threaded section of an interior of the distal bone
anchor; and threadedly advancing the second inter-anchor element in
a distal direction within the distal bone anchor to pull the
proximal bone anchor towards the distal bone anchor until the
distance between the distal bone anchor and the proximal bone
anchor is fixed.
Another set of teachings may be summarized by:
A method for setting a distance between a proximal bone anchor and
a distal bone anchor in adjacent vertebral bodies; the method
comprising: rotating a first inter-anchor element threadedly
engaged with the pair of bone anchors to use dissimilar thread
pitch to set the distance between the pair of bone anchors.
Another set of teachings may be summarized by compressing the
contents of an intervertebral disc space through reduction of the
distance between anchored bone anchors. The intervertebral disc
space may be merely compressed from the pre-therapy height of the
disc space or the disc space may have been temporarily
hyper-distracted before the compression.
Another set of teachings may be summarized by creation of an
assembly for implantation across two spinal vertebrae comprising: a
distal anchor for engagement with a distal vertebra; a proximal
anchor for engagement with a proximal vertebra; and a retraction
inducing element adapted to engage a shoulder within an interior of
the proximal anchor and to engage an interior of the distal anchor
such that rotation of the compression inducing element has a
capacity to reduce a distance between the distal anchor and the
proximal anchor.
Another set of teachings may be summarized as the fabrication of
the components and assembly of completed combinations of components
shown in the various drawings.
This summary is meant to provide an introduction to the concepts
that are disclosed within the specification without being an
exhaustive list of the many teachings and variations upon those
teachings that are provided in the extended discussion within this
disclosure. Thus, the contents of this summary should not be used
to limit the scope of the claims that follow.
Inventive concepts are illustrated in a series of examples, some
examples showing more than one inventive concept. Individual
inventive concepts can be implemented without implementing all
details provided in a particular example. It is not necessary to
provide examples of every possible combination of the inventive
concepts provided below as one of skill in the art will recognize
that inventive concepts illustrated in various examples can be
combined together in order to address a specific application.
Other systems, methods, features, and advantages of the disclosed
teachings will be or will become apparent to one with skill in the
art upon examination of the following figures and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within the scope of
and be protected by the accompanying claims.
BRIEF DESCRIPTION OF THE FIGURES
The disclosure can be better understood with reference to the
following figures. The components in the figures are not
necessarily to scale, emphasis instead being placed upon
illustrating the principles of the disclosure. Moreover, in the
figures, like reference numerals designate corresponding parts
throughout the different views.
FIG. 1 shows a lateral view of a portion of a human spine with a
two-level fusion assembly connected to three vertebrae and
traversing two adjacent intervertebral disc spaces.
FIG. 2 is an isometric view of a fusion rod.
FIG. 3 is a cross section of FIG. 2.
FIG. 4 is a view of the proximal end of the fusion rod.
FIG. 5 is a side view of a proximal anchor.
FIG. 6 is a cross section view of FIG. 5.
FIG. 7 is a perspective view of proximal anchor looking from the
proximal end towards the distal end.
FIG. 8 provides a side view of a spanning distraction rod.
FIG. 9 is a cross section of FIG. 8 and shows a driver engagement
section.
FIG. 10 shows a distal end view looking towards the proximal end of
the spanning distraction rod.
FIG. 11 is a side view of a fixation rod.
FIG. 12 is a cross section of FIG. 11.
FIG. 13 is a cross section of partial assembly that includes the
fusion rod, the proximal anchor, and the spanning distraction
rod.
FIG. 14 shows the partial assembly of FIG. 13 after the spanning
distraction rod has been retracted.
FIG. 15 shows the components from FIG. 13 after the insertion of
fixation rod 800.
FIG. 16 is a flow chart for a process of implanting a two-level
fusion assembly.
FIG. 17 is a process to set distraction distance.
FIG. 18 shows a lateral view of a two-level fusion assembly engaged
with three adjacent vertebrae.
FIG. 19 provides cross sections of the three anchors show in FIG.
18.
FIG. 20 the distal spanning distraction rod, the proximal spanning
distraction rod, and the three anchors from FIG. 18.
FIG. 21 illustrates the completed subassembly after insertion of
the distal fixation rod.
FIG. 22 shows the addition of proximal spanning distraction rod to
the sub-assembly of FIG. 21.
FIG. 23 shows the addition of the proximal fixation rod to the
sub-assembly of FIG. 21.
FIG. 24 is a flow chart for the process of compressing inserted
material within an intervertebral disc space.
FIG. 25 is a cross section view of an assembly using a single
fixation rod.
FIG. 26 is a cross section of a sub-assembly before the addition of
the fixation rod.
FIG. 27 is the cross section of FIG. 26 after the addition of the
fixation rod.
FIG. 28 is a cross section of a sub-assembly before the addition of
the stabilization rod.
FIG. 29 is the cross section of a sub-assembly show in FIG. 28
after the addition of the stabilization rod.
FIG. 30 is a cross section of an assembly with a dual threaded
spanning distraction rod.
DETAILED DESCRIPTION
FIG. 1 shows a lateral view of a portion of a human spine with a
two-level fusion assembly 100 connected to three vertebrae and
traversing two adjacent intervertebral disc spaces. FIG. 1 omits
the biological structures of the spine not relevant to the present
disclosure.
The three vertebrae may be called, the distal vertebral body 404
(or the distal vertebra), medial vertebral body 408 (or the medial
vertebra), and proximal vertebral body 412 (or the proximal
vertebra). The intervertebral space between the distal vertebral
body 404 and the medial vertebral body 408 may be called the distal
intervertebral disc space 416. Likewise the intervertebral space
between the medial vertebral body 408 and the proximal vertebral
body 412 may be called the proximal intervertebral disc space 420.
In a trans-sacral procedure, the access channel 212 for the
preparation and implantation is accessed from the sacrum located at
the caudal end of the spine and thus the concepts of proximal and
distal are taken with respect to the trans-sacral access.
The three vertebrae may be the L4, L5, and S1 vertebrae. The S1
vertebra is the top portion of the sacrum which is fused from
several individual components including S1. The teachings of the
present disclosure may be used in other pairs of motion segments
and thus the three vertebrae represented in FIG. 1 may be L3, L4,
and L5 or possibly an even more cephalad pair of adjacent motion
segments. One of skill in the art will recognize that three or more
adjacent motion segments could be provided therapy such that there
would be more than one medial vertebra and more than two treated
intervertebral disc spaces.
Various details of the two-level fusion assembly are visible in
FIG. 1. The major components described in greater detail below are
the fusion rod 500, proximal anchor 600, and a portion of spanning
distraction rod 700. As described below, a small portion of the
fixation rod 800 (not labeled in FIG. 1) is visible through the set
of ports 528.
FIG. 2 and FIG. 3 show a fusion rod 500 with a distal thread 504
and a proximal thread 508. The proximal and distal threads 504 and
508 may be placed substantially in two adjacent vertebrae. (Note
while a view of a threaded rod in cross section appears to have a
set of threads, typically there is one helical thread that travels
over the surface of the threaded rod). Because of the significant
differences in the major diameters of the two threads, the two
threads may have different thread pitches without a risk of
cross-threading or a need for timed delivery. Thread pitch, as used
herein, is the distance between corresponding points on a thread.
This concept is easy to see in a cross section such as FIG. 3 and
is shown by distance 512. The thread pitch of the distal thread 504
is the same as the thread pitch of the proximal thread 508. Thread
pitch is frequently described in terms of threads per inch or
TPI.
While the example of the fusion rod 500 shown in FIG. 2 and FIG. 3
uses the same thread pitch for the distal thread 504 and the
proximal thread 508, dissimilar thread pitches may be used in order
to provide distraction.
Use of Dissimilar Thread Pitch in Fusion Rod
The use of dissimilar thread pitches to distract vertebral bodies
within a single motion segment is described in commonly assigned
U.S. Pat. No. 6,921,403 "Method and Apparatus for Spinal
Distraction and Fusion" issued on Jul. 26, 2005 filed on that same
date, which are herein incorporated in their entirety by reference
into this disclosure.
Dissimilar thread pitch may be used to provide a predictable amount
of distraction of a motion segment as the distraction is a function
of the ratio of the thread pitches. For example if the distal
thread has a pitch of 12 thread peaks per inch (typically called
threads per inch) and the proximal thread has a pitch of 10 thread
peaks per inch, then when the rod is engaged with the two adjacent
vertebrae, distraction will occur during rotation of the rod. More
specifically, when the rod is rotated in the appropriate direction
for the handedness of the threads, the rod will move distally 1
inch into the distal vertebra with 12 rotations of the rod driver.
However, these same 12 rotations of the rod driver will advance the
rod relative to the proximal vertebra 1.2 inches. Thus, the
distance between the two vertebrae will be increased 0.2
inches.
All other things being kept equal, choosing a larger difference in
thread pitch makes it possible to produce a larger amount of
distraction.
Fusion rod 500 has a channel 516 that runs from the distal end 520
to the proximal end 524 and may be used to deliver the fusion rod
500 over a guide wire. The channel 516 is connected to a set of
ports 528 which may be used to deliver material to a disc
space.
Fusion rod 500 has an interior threaded section 532, a driver
engagement section 536, and a cylindrical section 540.
FIG. 2 and FIG. 3 shows the distal thread 504 increases in major
diameter from the distal end 520 towards the ports 528. A chip
breaking section 544 is visible towards the distal end of the
distal thread 504.
FIG. 4 shows the channel 516 as viewed from the proximal end 524
(FIG. 3) of the fusion rod 500. Note that the driver engagement
section 536 is not symmetric as one face 548 of the six faces of
the substantially hexagonal opening is rounded rather than flat.
The purpose of face 548 will be discussed below.
Proximal Anchor
FIG. 5 shows a proximal anchor 600. The proximal anchor 600 has an
external thread 604. The proximal anchor 600 has a channel 616 that
runs from the proximal end 612 to the distal end 608.
FIG. 6 is a cross section of FIG. 5. The cross section shows
internal thread 620 and a set of notches 624 in the internal thread
620.
FIG. 7 is a perspective view of proximal anchor 600 looking from
the proximal end towards the distal end. Internal thread 620 is
visible as are the sets of notches 624. Note that one set of
notches, 628, is a different shape from the other sets of notches.
The notch set 628 and face 548 (FIG. 4) of the fusion rod 500 (FIG.
4) may be used to align the fusion rod 500 and the proximal anchor
600 on a common driver so that the two components may be delivered
by timed delivery so that the external thread 604 may be sized with
the same major diameter and thread pitch as the proximal thread 508
on the fusion rod 500. Timed delivery allows the second thread to
travel in the thread path created by an earlier thread and do so
without cross threading.
Spanning Distraction Rod
FIG. 8 provides a side view of a spanning distraction rod 700.
External thread 704 is located near the proximal end 724. Distal
portion 708 is shown with optional flutes (discussed below). The
spanning distraction rod 700 has a channel 720 that runs through
the spanning distraction rod 700 from proximal end 724 to distal
end 716.
Optional band 712 may be used to provide a visual indicator for use
in the process of assembling components for delivery by a driver in
order to prevent the spanning distraction rod 700 from altering the
spacing between the fusion rod 500 and the proximal anchor 600 on
the dual driver as this would alter the timing of the threads
between the two anchors. The band 712 may be a different color or
texture than other portions of the distal portion 708.
FIG. 9 is a cross section of FIG. 8 and shows a driver engagement
section 728.
FIG. 10 shows a distal end view looking towards the proximal end of
the spanning distraction rod 700. The driver engagement section 728
is visible within channel 720 surrounded by the rounded distal end
716. The driver engagement section is substantially a hexagonal
socket but two faces 736 are round rather than flat.
Comparing FIG. 10 to FIG. 4, one can see that a driver may be made
with a single rounded face that would engage both spanning
distraction rod 700 and fusion rod 500. However a second driver
head with two rounded faces would drive only the spanning
distraction rod 700 but not the fusion rod 500.
Returning to FIG. 10, the set of flutes 732 is visible. Fluting the
distal portion 708 (FIG. 8) of spanning distraction rod 700 reduces
the amount of surface area to make contact between the spanning
distraction rod 700 and the internal walls of the fusion rod 500.
Thus, the fluted distal portion 708 (FIG. 8) of the spanning
distraction rod 700 may be rotated relative to an implanted fusion
rod 500 while reducing the risk of inadvertently rotating the
fusion rod 500 and changing the position of the fusion rod 500
relative to the distal vertebral body 404 (see FIG. 1) and the
medial vertebral body 408 (FIG. 1). Avoiding unintended rotation of
the fusion rod 500 is particularly desirable for fusion rods with
dissimilar thread pitch as rotation causes a change in distraction
of the distal motion intervertebral space 416 (see FIG. 1).
Fixation Rod
FIG. 11 is a side view of a fixation rod 800. FIG. 12 is a cross
section of FIG. 11. Fixation rod 800 has an external thread 804
near the distal end 808. A driver engagement section 812 is open at
the proximal end 824 of the fixation rod 800. The driver engagement
section 812 may be combined with an internal threaded bore 816 for
use with a threaded retention rod in an appropriate driver to
retain the fixation rod 800 to the driver. The fixation rod 800 has
a shoulder 820 near the proximal end to engage a corresponding
feature at the proximal end 724 of the spanning distraction rod 700
(FIG. 8).
Setting the Minimum Distance Between Vertebrae
FIG. 13 is a cross section of partial assembly that includes the
fusion rod 500, the proximal anchor 600, and the spanning
distraction rod 700. Referencing now FIG. 1 and FIG. 13, these
three components may be delivered simultaneously by one common
driver into an access channel 212 that has been prepared including
packing the proximal intervertebral disc space with bone chips and
other fusion promoting material. Engagement of the sets of notches
624 accessible from the proximal end of the proximal anchor 600 can
preclude unintentional rotation and advancement of the proximal
anchor 600 relative to the proximal vertebral body 412. An
appropriate driver may be used to advance the spanning distraction
rod 700 relative to the proximal anchor 600 using threaded
engagement of the threaded section 704 of the spanning distraction
rod 700 with the internal thread 620 in the proximal anchor
600.
Rotation and advancement in the distal direction of the spanning
distraction rod 700 causes the rounded distal end 716 to contact
the fusion rod 500 and to push the fusion rod 500 to increase the
distance between the proximal vertebral body 412 anchored to the
proximal anchor 600 and the medial vertebral body 408 anchored to
the fusion rod 500. Selection of components of known lengths and
arrangements allows the movement of the spanning distraction rod to
be a means for increasing distraction of an intervertebral space by
setting a minimum distance between the proximal anchor 600 and the
fusion rod 500 and thus allows for the controlled increase in the
space between the proximal vertebral body 412 and the medial
vertebral body 408.
Reducing the Intervertebral Disc Space Height
Sometimes a surgeon may advance the spanning distraction rod 700 to
impose a first distraction and after evaluation of the fluoroscopic
images, may decide that a decrease in imposed distraction is
appropriate. While not a frequent occurrence, a surgeon may want to
decrease the height of an intervertebral disc space from the
pre-surgery height. In either case, the surgeon is looking to
reduce the height of the intervertebral disc space.
FIG. 14 shows the partial assembly of FIG. 13 after the spanning
distraction rod 700 has been retracted such that the threaded
portion 704 has moved in the proximal direction along internal
threads 620 to introduce a gap 104 between the rounded distal end
716 of the spanning distraction rod 700 and the fusion rod 500.
FIG. 15 shows the assembly after the insertion of fixation rod 800.
An appropriate drive imparting torque to the driver engagement
section 812 will cause the fixation rod 800 to spin relative to the
proximal anchor 600 without moving in the proximal/distal
direction. FIG. 15 shows the contact between shoulder 820 of the
fixation rod 800 and the proximal end 724 of spanning distraction
rod 700.
As the threaded section 804 engages the internal threaded section
532 of the fusion rod 500, the fusion rod 500 is pulled towards the
proximal end 824 of the fixation rod 800 and the proximal anchor
600. With sufficient rotation of the fixation rod 800, the rounded
distal end 716 of the spanning distraction rod 700 makes solid
contact with the fusion rod 500. Now the minimum distance between
the proximal anchor 600 and the fusion rod 500 is maintained by the
spanning distraction rod 700 and the fixation rod 800 can be used
to hold the distance between the proximal anchor 600 and the fusion
rod 500 at no more than that minimum distance.
One of skill in the art will recognize that tightening the fixation
rod 800 after the components have made contact will stretch the
fixation rod 800 to put the fixation rod 800 in tension and help
reduce any tendency to come loose by rotation. Excessive tightening
may transfer torque to the thread bone interfaces or impart an
unwanted rotation to the fusion rod.
Process of Implanting Assembly
As the process of creating an access channel for use in a
trans-sacral procedure has been covered in detail in a number of
published patent applications and issued patents assigned to the
assignee of this application, the process of creating a channel and
preparing a set of vertebrae with bore holes of appropriate size
for a given implant and thread will not be repeated here. The
relevant information for the present disclosure with respect to
two-level fusion assembly 100 may be summarized as set forth in
FIG. 16 as process 1000.
1006--Prepare Access Channel A number of earlier applications with
common assignee have addressed formation of a trans-sacral access
channel 212 (FIG. 1). One of skill in the art will recognize that
the specific bore sizes used for the access channel will be a
function of the size components to be placed into the vertebral
bodies and the desired difference between bore size and minor
diameter of the threaded anchor to be placed in that vertebra.
Examples of applications with material illustrating examples of
access channel preparation may be found in U.S. Pat. No. 7,087,058
for Method and Apparatus for Providing Posterior or Anterior
Trans-Sacral Access to Spinal Vertebrae and U.S. Patent Application
Publication US-2007-0168036-A1 for Spinal Motion Preservation
Assemblies (See FIG. 13). Both documents are incorporated by
reference herein. One of skill in the art will recognize that the
preparation of a disc space for fusion will be different than
preparation for insertion of a motion preservation device as
preparation for fusion may purposefully seek to cause bleeding of
the vertebral endplates to promote fusion.
1012--Select Components. While the surgeon may have estimated the
approximate size of the various components to be used in the
two-level fusion assembly, the final selection amongst the
available nominal sizes for components may be made during surgery
given the feedback available to the surgeon from fluoroscopic
imaging and from the opportunity to insert objects that serve as
trials for inserting components of particular sizes.
1018--Pack the Proximal Intervertebral Space. After the disc
material has been removed and the endplates have been prepared to
promote fusion, the disc space may be filled with bone chips or
other fusion promoting materials. Surgeons have used bone chips,
including bone material removed from the patient during the
creation of the bores through the vertebrae (autologous bone
material) for this process. Some surgeons add other materials to
the bone material to promote fusion. The particular choices used
for packing the intervertebral space are beyond the scope of this
disclosure but are known to those of skill in the art.
1024--Prepare Beyond the Proximal Intervertebral Space. Prepare the
bore in the medial vertebral body 408. Prepare the distal
intervertebral space 416 for fusion including packing with fusion
promoting material such as bone chips. Prepare the bore in the
distal vertebral body 404. The process of preparing the bores may
include the insertion of objects that represent implants or provide
markers to help in the selection of an implant of a particular size
for the geometries of this particular surgery. This process may
cause the surgeon to adjust the preliminary selections for implant
sizes. Placing the trial objects in the bore may serve to dilate
the bore.
1030--Load the Dual Driver. Thread the spanning distraction rod 700
into the proximal anchor 600 such that the spanning distraction rod
700 extends beyond the proximal anchor 600 a desired amount. The
use of band 712 facilitates this process, although this band is not
required. When loaded onto the driver with the fusion rod 500 and
proximal anchor 600 engaged via keys with the driver and separated
by a known distance (such as abutting), the proximal thread 508 of
the fusion rod 500 and the external thread 604 of the proximal
anchor 600 may be delivered by timed delivery so that the two
threads of the same size are not cross threaded. As the maximum
major diameter of the tapered thread on the distal thread 504 of
fusion rod 500 is small enough to pass through the bores in the
medial vertebral body 408 and the proximal vertebral body 412
without causing problems for the subsequent introduction of the
larger threads, the delivery of distal thread 504 does not need to
be done by timed delivery. As described in earlier applications and
patents, the use of a distal thread that has a smaller major
diameter than the proximal thread allows for distraction through
use of dissimilar thread pitch.
A retention rod within the driver (not shown) may be engaged with
the interior threaded section 532 of the fusion rod 500 to pull the
fusion rod 500 tight onto the driver and against the proximal
anchor 600.
1036--Deliver the Fusion Rod and Proximal Anchor. The spanning
distraction rod 700 is on the driver and between the fusion rod 500
and proximal anchor 600. The driver and components may be loaded
over a guide wire. The driver may threadedly advance the components
until the proximal anchor 600 is positioned appropriately with
respect to the proximal vertebral body 412. The positioning of the
proximal anchor 600 relative to the sacrum (if the sacrum is the
proximal vertebral body 412) may call for a portion of the external
thread 604 to protrude slightly on both the proximal and distal
ends of the bore in the sacrum.
1042--Remove the Dual Driver. If a retention rod was engaged with
the interior threaded section 532, this engagement will be
unthreaded before removal of the dual driver.
1048--Adjust Placement of the Fusion Rod. If desired, use a driver
that will pass through the interior of the spanning distraction rod
700 to engage the fusion rod 500 but not the proximal anchor 600.
In order to minimize damage to the thread/bone interface, it may be
preferred to avoid moving the fusion rod 500 proximally.
1054--Add Material to the Distal Intervertebral Space. Optionally,
additional material may be added to the previously packed distal
intervertebral space 420 through the set of ports 528 in the fusion
rod 500.
1060--Distract Proximal Intervertebral Space. Engage the set of
notches 624 with a counter torque tube or other device to preclude
unintended rotation of the proximal anchor 600. Insert driver
through the counter torque tube to engage the spanning distraction
rod 700 and advance the spanning distraction rod 700 to allow the
rounded distal end 716 of the spanning distraction rod 700 to push
against the anchored fusion rod 500 to increase the distance
between the medial vertebral body 408 and the proximal vertebral
body 412. This process may be characterized as a means for
distracting, that is increasing the distraction of the
intervertebral space by increasing the distance between the
anchors.
One of skill in the art will appreciate that the counter torque
tube could engage some other feature on the proximal end 612 of the
proximal anchor 600 instead of the set of notches 624, including
protuberances (this alternative is not shown) that extend
proximally from the proximal end of the proximal anchor. The set of
notches 624 or another feature accessible on the proximal face of
the proximal anchor serves as a means for engaging the proximal end
of the proximal anchor.
1066--Review Fluoroscope Images. If the amount of distraction
imposed by the spanning distraction rod 700 is too much, then
retract the spanning distraction rod 700 to leave a small gap 104
(FIG. 14) between the rounded distal end 716 and the fusion rod
500. The gap 104 will not be visible in fluoroscopic images as it
will be internal to the fusion rod 500. However, the distance will
be known (less any shifting of the vertebrae) as a function of the
thread pitch and the number of turns that the spanning distraction
rod 700 is retracted. The ability of the fixation rod 800 to
eliminate a hyper-distraction gap is limited by the length of the
threaded section with the external thread 804. In other words, the
gap (FIG. 14 element 104) cannot be so wide that the fixation rod
800 is unable to engage the internal threaded section 532 of the
fusion rod 500. The same would be true if the surgeon desired to
reduce the pre-surgery disc space height.
One of skill in the art will appreciate that extending the linear
distances for the external thread 804 and threaded section 532
increase the ability to decrease intervertebral disc space
height.
1072--Insert Fixation Rod and Tighten. The fixation rod 800 may be
retained on the driver by a retention rod that engages the internal
threaded bore 816. The external thread 804 engages the internal
threaded section 532 of the fusion rod 500. Optionally, the length
of the fixation rod may be set to extend up to the set of ports 528
in the fusion rod to prevent ingress of material from the distal
intervertebral space 420 (FIG. 1) through the ports 528 into the
fusion rod 500.
As shown in FIG. 15, the fixation rod 800 for use in a particular
combination of components may be designed so that the distal end
808 of the fixation rod 800 fills the fluoroscopic image of the
ports 528 when the fixation rod 800 is fully inserted. This
combination of component geometries allows the surgeon to confirm
position of the fixation rod 800 using fluoroscopy. Thus, the
assembly has a means for confirming the position for the fixation
rod tip.
The insertion of the fixation rod 800 will remove the gap 104
introduced by inadvertent hyper-distraction of the proximal
intervertebral disc space 420 (FIG. 1). This process may be
characterized as a means for retracting, that is reducing the
amount of distraction in an intervertebral space by reducing the
distance between anchors.
The fixation rod 800 may be tightened a prescribed amount such as
finger tight or to another set amount of torque based upon a
balance against wishing to tighten the two-level fusion assembly
100 and a desire not to cause unwanted consequences to the
engagements of threads with the vertebral bodies.
1078--Remove Fixation Rod Driver. This may include unthreading a
retention rod.
1084--Close Surgical Site. This step may include removal of a guide
wire and a cannula docked to the sacrum in addition to closing the
surgical access path.
Process to Set Distraction Distance
FIG. 17 highlights the process 1100 to set the distraction in the
proximal intervertebral space 420.
1106--Position Distal and Proximal Anchors. The fusion rod 500 and
the proximal anchor 600 serve as the distal and proximal anchors
across the proximal intervertebral space 420.
1112--Distract. The spanning distraction rod 700 may be threadedly
advanced relative to the proximal anchor 600 to push upon the
distal anchor (in this case fusion rod 500) to increase the minimum
distance between the two anchors and thus increase the distance
between the adjacent vertebral bodies threadedly engaged with the
two anchors.
1118--Adjust Minimum Distraction. Based upon review of fluoroscope
images or other surgical reasons, reduce the minimum distraction
imposed by the spanning distraction rod 700 by reversing a portion
of the threaded advance of the spanning distraction rod 700
relative to the proximal anchor 600. Not every surgical procedure
will include an adjustment of the minimum distraction but the
availability of this step facilitates the surgical process as the
surgeon can dial in the optimal distraction by trying a range of
distractions and viewing the results in fluoroscopic images.
1124--Retract and Hold. The addition of the fixation rod 800 that
pulls the two anchors together allows the retraction (reduction of
distraction) if needed and pulls the assembly together. The
distance between the two anchors is now held by the combination of
pushing and pulling.
Three Anchor Solution
A second two-level fusion assembly 2000 is shown in a lateral view
of a portion of a human spine placed in three adjacent vertebrae in
FIG. 18. FIG. 18 is not a cross section but rather a view of the
spinal implant visible within the spine somewhat like a fluoroscope
image. As with FIG. 1, FIG. 18 omits biological structures of the
spine not relevant to the present disclosure. As with FIG. 1, a
portion of a spine is represented by distal vertebral body 404,
medial vertebral body 408, proximal vertebral body 412, distal
intervertebral space 416, and proximal intervertebral space
420.
Visible in FIG. 18 are the three anchors: distal anchor 2100,
medial anchor 2200, and proximal anchor 2300. Partially visible in
FIG. 18 are the distal spanning distraction rod 2400 and the
proximal spanning distraction rod 2500. As will become evident upon
study of subsequent figures, partially visible though the large
ports (discussed below) but not recognizable are the distal
fixation rod and the proximal fixation rod.
FIG. 19 provides cross sections of the three anchors. The distal
anchor 2100 has an external thread 2104, a driver engagement
section 2108, and a threaded bore 2112 which may be used with a
retention rod to hold the distal anchor 2100 to a driver. A
shoulder 2116 is at the distal end of a cylindrical cavity 2120
that is open at the proximal end 2128 of the distal anchor 2100.
The distal anchor 2100 may be placed over a guide wire as it is
open from the proximal end 2128 to the distal end 2124.
The medial anchor 2200 has an exterior thread 2204. The interior of
the medial anchor 2200 is open from the distal end 2208 to the
proximal end 2212. The interior has a threaded section 2216 with
sets of notches 2220 that may be engaged by a driver.
The proximal anchor 2300 has an external thread 2304 and is open in
the interior from the distal end 2308 to the proximal end 2312. The
interior has a threaded section 2316 with sets of notches 2320 that
may be engaged by a driver. Medial anchor 2200 and proximal anchor
2300 may use the same major diameter and thread pitch such that the
proximal anchor may be delivered via timed delivery to engage into
a thread path previously cut by the medial anchor 2200 as the
medial anchor 2200 was advanced through the proximal vertebral body
412 (FIG. 18).
Medial anchor 2200 and proximal anchor 2300 differ principally in
length. A system of components could be implemented so that a
surgeon may pick appropriate anchors from a set of anchors of
different lengths to become the medial and proximal anchors for a
given procedure. Thus a particular size of anchor used as a medial
anchor for one patient may be used as a proximal anchor for a
different patient.
FIG. 20 shows the three anchors (2100, 2200, and 2300). FIG. 20
also shows the distal spanning distraction rod 2400 and the
proximal spanning distraction rod 2500.
Distal spanning distraction rod 2400 has an external thread 2404,
shoulder 2408, and fluted section 2412. The distal spanning
distraction rod 2400 has an interior channel (shown below) from the
proximal end 2424 to the distal end 2416. Distal spanning
distraction rod 2400 also has a set of large ports 2420.
Proximal spanning distraction rod 2500 has an external thread 2504.
The proximal spanning distraction rod 2500 has an interior channel
(shown below) from the proximal end 2524 to the distal end 2516.
Proximal spanning distraction rod 2500 also has a set of large
ports 2520.
These large ports (2420 and 2520) may be used with an appropriate
tool to deliver fusion promoting material (such as bone chips) to
the intervertebral disc space. The process of delivering fusion
promoting material may include rotating the spanning distraction
rod ninety degrees to allow the ports to face a greater range of
directions in the intervertebral disc space.
One of skill in the art will recognize that a single port may be
used on a spanning distraction rod along with perhaps a greater
need to rotate the single port to deliver the material.
Alternatively three or more ports could be used instead of two
ports as shown here.
Fixed Distraction of Distal Space
FIG. 21 illustrates the completed subassembly after insertion of
the distal fixation rod 2600 after delivery of material to the
distal intervertebral disc space through the large ports (2420 in
FIG. 20). An option open to surgeons, is to purposefully
hyper-distract the distal intervertebral disc space (416 in FIG.
18) to facilitate the delivery of material into the oversized gap
between the distal vertebral body (404 in FIG. 18) and the medial
vertebral body (408 in FIG. 18).
One of skill in the art will appreciate that one could use the
large ports 2420 to deliver devices to the intervertebral disc
space including small fusion cages, spherical cages, expandable
cages, balloons, and other devices that would assist in the process
of creating a stable fused space. Likewise, one could deliver
devices to the intervertebral disc space including small fusion
cages, spherical cages, expandable cages, balloons, and other
devices to the hyper-distracted disc space through any of the
non-trans-sacral surgical approaches known in the art of spinal
surgery.
One of skill in the art will appreciate that after the disc space
is distracted or hyper-distracted there are options to introduce
tools of various types into the disc space that may not have fit
within an unusually thin disc space. Thus, after distraction or
hyper-distraction, one could use the large ports 2420 to provide
access to the intervertebral disc space for introduction of the
distal end of tools such as: surgical instruments to further
prepare the disc space, visualization instruments, or other tools
that would assist in the process of providing therapy. Likewise,
after distraction or hyper-distraction, one could introduce:
surgical instruments to further prepare the disc space,
visualization instruments, or other tools that would assist in the
process of providing therapy space through any of the
non-trans-sacral surgical approaches known in the art of spinal
surgery.
After filling, the distal spanning distraction rod 2400 could be
rotated by a driver interacting with the driver engagement section
of the distal spanning distraction rod 2400 located in the proximal
end of the spanning distraction rod 2400 analogous to the driver
engagement section for proximal spanning distraction rod 2500 (see
element 2530 in FIG. 22). Referencing FIG. 21, rotation in the
appropriate direction based on the thread handedness would move the
external thread 2404 relative to the threaded section 2216 of
medial anchor 2200 to back off the hyper-distraction by a
predictable distance based on number of turns and thread pitch.
Distal Fixation Rod
The distal fixation rod 2600 is visible in FIG. 21. The distal
fixation rod 2600 has: a distal end 2604, a proximal end 2608, a
driver engagement section 2612, a threaded bore 2616 for use with a
retention rod, and a threaded section 2620 near the distal end
2604.
Insertion and rotation of the distal fixation rod 2600 engages the
threaded section 2620 with the threaded bore 2112 of the distal
anchor 2100. When tightened, the distal fixation rod 2600 will pull
the two anchors (2100 and 2200) together to the minimum distraction
distance set by the position of the distal spanning distraction rod
2400 within the medial anchor 2200.
By choice of component lengths a designer may choose to have the
proximal end 2128 of the distal anchor 2100 rest firmly against the
shoulder 2408 of the distal spanning distraction rod 2400.
Alternatively, the distal end 2416 of the distal spanning
distraction rod 2400 will rest against shoulder 2132 of the distal
anchor 2100.
The movement of the endplates of the two vertebral bodies (404 and
408) anchored to the two anchors (2100 and 2200) will compress
material used to fully fill a hyper-distracted distal
intervertebral disc space 416. Compression may promote fusion by
either accelerating the process or increasing the likelihood of
successful fusion.
One theory supporting the use of compression is Wolff's law which
suggests that bone forming cells, osteoblasts, require loading in
order to promote growth.
Whether or not the use of the distal fixation rod 2600 removes
intentional hyper-distraction added to allow compression of
inserted material, or removes unintended hyper-distraction from a
process of testing various distraction amounts via fluoroscopy as
discussed above, the use of the distal fixation rod 2600 will lock
that portion of the assembly so that the distance between the two
anchors (2100 and 2200) is fixed.
Fixation of the distance between the anchors may be advantageous
when a patient is undergoing several different procedures during
one surgical session and must be repositioned. Repositioning a
substantially lateral patient (without gravity to press the
vertebrae downward) could potentially change the distance between
adjacent vertebrae unless prevented by the presence of the fixation
rod. Fixation may serve other patients in other ways.
Another advantage of fixation is that may provide an extra layer of
protection to eliminate any slight risk of the proximal anchor
migrating away from the rest of the assembly
Adding Distraction to the Proximal Motion Segment
After fixation of the distraction in the distal intervertebral
section, the proximal intervertebral disc space (420 in FIG. 18)
may be addressed. FIG. 22 shows the addition of proximal spanning
distraction rod 2500 to the sub-assembly of FIG. 21. Proximal
spanning distraction rod 2500 has a driver engagement section 2530
at the proximal end 2524.
Rotation of the proximal spanning distraction rod 2500 through use
of a driver engaged with the driver engagement section 2530 will
advance the external thread 2504 relative to the threaded section
2316 of the proximal anchor 2300. Advancing the proximal spanning
distraction rod 2500 will cause the distal end 2516 of the proximal
spanning rod 2500 to push against the proximal end 2608 of the
distal fixation rod 2600 to push the sub-assembly including the
medial anchor 2200 and the distal anchor 2100 away from the
proximal anchor 2300.
As discussed above in connection with the use of distal spanning
distraction rod 2400, the large ports 2520 may be used to deliver
material to the proximal intervertebral disc space (420 in FIG.
18), including the rotation of the ports by ninety degrees to
facilitate delivery to all portions of the intervertebral disc
space.
As discussed above there may be inadvertent hyper-distraction as
the surgeon seeks to dial in the optimal spacing between anchors
and tests a proposed position of the proximal spanning distraction
rod 2500 that provides too much distraction based upon an
evaluation of the positioning via fluoroscopy. As mentioned above,
the proximal intervertebral disc space may be intentionally
hyper-distracted in order to allow overfilling of the oversized
proximal intervertebral disc space (420 in FIG. 18) so that the
filling material may be compressed.
Proximal Fixation Rod
The proximal fixation rod 2700 is visible in FIG. 23. The proximal
fixation rod 2700 has: a distal end 2704, a proximal end 2708, a
driver engagement section 2712, a threaded bore 2716 for use with a
retention rod, and a threaded section 2720 near the distal end
2704.
Insertion of the proximal fixation rod 2700 engages the threaded
section 2720 with the threaded bore 2616 of the distal fixation rod
2600. When tightened, the proximal fixation rod 2700 will decrease
the distance between the proximal anchor 2300 and the other two
anchors (2100 and 2200) to the minimum distraction distance set by
the position of the proximal spanning distraction rod 2500 within
the proximal anchor 2300.
The proximal end 2608 of the distal fixation rod 2600 will rest
firmly against the distal end 2516 of the proximal spanning
distraction rod 2500.
If the intervertebral disc space was hyper-distracted and fully
filled, the movement of the endplates of the two vertebral bodies
(408 and 412) anchored to the two anchors (2200 and 2300) will
compress material used to fully fill the hyper-distracted proximal
intervertebral disc space 420.
Method of Overfilling and Compressing Material
FIG. 24 provides a short flow chart to summarize the process 1200
of compressing inserted material within an intervertebral disc
space.
1206--Position Anchors. Position a pair of anchors into the two
adjacent vertebrae on either side of an intervertebral disc
space.
1212--Impose Hyper-Distraction. By hyper-distraction it is meant
that the minimum distance between anchors is temporarily set at a
larger value than desired in the final assembly.
1218--Insert Material. Insert material into the intervertebral disc
space. As the anchors are connected to the two vertebrae and the
two anchors are positioned in a hyper-distracted distance apart
from one another, the intervertebral disc space has a larger
distance between vertebrae than desired in the final assembly.
Filling this disc space full of material makes compression
possible. The material may include bone chips and material to
promote bone growth. The material may include various devices that
may help promote stability or structural support. Thus, the
material may include fusion cages or other man-made devices.
The inserted material may come from a trans-sacral route or through
a non-trans-sacral route.
1224--Compress. Use of a fixation rod pulls the anchors towards one
another and thus pulls the two vertebrae towards one another to
reduce the space between the vertebrae. The compression of material
placed in the intervertebral disc space may promote the fusion
process by increasing contact, collapsing any voids in the inserted
material, encouraging bone growth by the imposition of the
compressive stress, and providing other benefits.
Use of Single Fixation Rod for Three Anchors
FIG. 25 has a different configuration with single fixation rod 2900
that connects the distal anchor 2100 to the proximal anchor 2300.
As this configuration has some commonalities with the
configurations discussed above, this description will be brief.
The minimum distance between distal anchor 2100 and medial anchor
2200 may be set through use of distal spanning distraction rod 2400
through contact by the distal end 2416 with the interior of the
distal anchor 2100 or by contact between the shoulder 2408 with the
proximal end 2128 of the distal anchor 2100 (or by a combination of
both contacts). Most likely, through just the contact provided by
the distal end 2416 by adjusting dimensions so that the distal end
2416 makes contact first.
The minimum distance between the medial anchor 2200 and the distal
anchor 2100 may be controlled by rotating the distal spanning
distraction rod with a driver that interacts with a driver
engagement section (hidden in this cross section by 2900) in the
proximal end 2424 of the distal spanning distraction rod 2400 to
threadedly advance the distal spanning distraction rod 2400
relative to the medial anchor 2200. As described above, the large
ports 2420 (visible here based on the cross section taken) may be
used to deliver material to the distal intervertebral disc space
(416 of FIG. 18). The spanning distraction rod 2400 may have a
fluted section as discussed above.
Long Proximal Spanning Distraction Rod
Continuing to refer to FIG. 25, long proximal spanning distraction
rod 2800 may be used to impose a minimum distance between the
proximal anchor 2300 and the medial anchor 2200 through threaded
advancement of the external thread 2804 of the long proximal
spanning distraction rod 2800 and the threaded section 2316 of the
proximal anchor 2300. Threaded advancement is controlled by the use
of an appropriate driver to engage a driver engagement section 2830
in the proximal end 2824 of the long proximal spanning distraction
rod. Threaded advancement of the long proximal spanning distraction
rod 2800 causes contact and pushing between the distal end 2816 and
the proximal end 2424 of the distal spanning distraction rod
2400.
The long proximal spanning distraction rod 2800 may have large
ports (not visible in this cross section) which may be used to
deliver material to the proximal intervertebral disc space (420 in
FIG. 18).
Single Fixation Rod
FIG. 25 shows the assembly after insertion of the single fixation
rod 2900. Single fixation rod 2900 has an external thread 2920 at
the distal end 2904 that engages with the threaded bore 2112 of the
distal anchor 2100. Single fixation rod 2900 may be rotated through
use of a driver that engages a driver engagement section 2912 at
the proximal end 2908 and optionally engages a threaded bore 2916
with a retention rod.
The use of a single fixation rod 2900 does not provide the
flexibility afforded by the use of two fixation rods and thus is
not as well adapted to provide compression of material provided to
each of the two intervertebral disc spaces. The single fixation rod
2900 may remove small amounts of hyper-distraction induced by
processes that rotate the large ports to provide improved access to
the disc space while using the large ports to deliver material to
the disc space.
One Level Assembly
FIG. 26 and FIG. 27 show assembly 3000 with a distal anchor 3100,
proximal anchor 3200 spanning distraction rod 3400, and fixation
rod 3600. FIG. 26 shows the partial assembly before the addition of
the fixation rod 3600. FIG. 27 shows the completed assembly 3000
after the addition of the fixation rod 3600.
The one level assembly shown in FIG. 26 and FIG. 27 has some
similarities to FIG. 21 that showed a partial assembly of a
two-level modular assembly. More specifically, FIG. 21 showed the
components associated with setting the intervertebral distance for
the distal intervertebral space. The major components in FIG. 21
are the distal anchor 2100, medial anchor 2200, distal spanning
distraction rod 2400, and distal fixation rod 2600.
Details present in FIG. 26 include the external thread 3404 near
the proximal end 3424 of the spanning distraction rod 3400, driver
engagement section 3432, portions of the large ports 3420, shoulder
3408 which may be designed to contact proximal end 3116 of distal
anchor 3100.
As with examples discussed above, the combination of the spanning
distraction rod 3400 and fixation rod 3600 sets the distance
between the distal anchor 3100 and proximal anchor 3200.
Frequently, a single level therapy will be applied to the L5/S1
motion segment. In contrast, the distal motion segment for a
multi-level therapy cannot be the L5/S1 motion segment if the
approach route is a trans-sacral route as L5/S1 is the most
proximal motion segment. Thus, one difference that appears in the
example shown in FIG. 26 and FIG. 27 versus what is shown in FIG.
21 is that the anchors are sized for placement in S1 and L5 rather
than L5 and L4.
A second difference is that the spanning distraction rod 3400
occupies a greater percentage of the interior of proximal anchor
3200 than does the distal spanning distraction rod 2400 with
respect to the medial anchor 2200. Likewise the fixation rod 3600
occupies a substantial portion of the interior of proximal anchor
3200. As proximal anchor 3200 is not a medial anchor involved with
two motion segments, there is no need for the proximal anchor 3200
to have space to receive a proximal spanning distraction rod or a
proximal fixation rod.
Use of Dissimilar Thread Pitch
An alternative to using a spanning distraction rod that is threaded
on the proximal end only and used to push the distal anchor, is a
spanning distraction rod that is threaded on both the proximal and
distal ends and uses dissimilar thread pitch to provide a
controlled distraction. The concept of dissimilar thread pitch was
discussed above in connection with the use on a distraction
rod.
FIG. 28 shows a distal anchor 4100 with a threaded bore 4112 with a
first thread pitch and a proximal anchor 4200 with a threaded bore
4216 with a second thread pitch which will typically be finer than
the first thread pitch. Once the distal external thread 4428 of the
dual threaded spanning distraction rod 4400 is engaged with the
threaded bore 4112 of the distal anchor 4100 and the proximal
external thread 4404 is engaged with the threaded bore 4216 of the
proximal anchor 4200, application of torque to the driver
engagement section 4432 will alter the distance between the distal
anchor 4100 and the proximal anchor 4200. Rotation of the dual
threaded spanning distraction rod 4400 in one direction will
increase the distance between the anchors and rotation in the
opposite direction will decrease the distance between anchors.
FIG. 29 shows assembly 4000 with the addition of a stabilization
rod 4600. The stabilization rod 4600 may be rotated by an
appropriate driver through interaction with a driver engagement
section 4612. The driver may use a retention rod to engage a
threaded bore 4616. As the stabilization rod 4600 is rotated
relative to the distal anchor 4100, an external thread 4620 on the
stabilization rod 4600 engages an internal thread 4140 near the
distal end 4124 of the distal anchor 4100.
The stabilization rod 4600 augments the structure of the dual
threaded spanning distraction rod 4400 to compensate for the large
ports 4420 (FIG. 28) and to block the large ports 4420 (FIG. 28) to
prevent ingress of materials from the intervertebral disc space
into the interior of assembly 4000. The stabilization rod 4600
lacks a shoulder or other feature to pull the proximal anchor 4200
towards the distal anchor 4100. The stabilization rod 4600 does not
need a shoulder for that use as the dual threaded spanning
distraction rod 4400 sets the distraction distance as the dual
threaded spanning distraction rod 4400 has threaded engagement with
both anchors.
The amount of distraction that may be imposed by the dual threaded
spanning distraction rod 4400 will be a function of the difference
in thread pitch between the distal external thread 4428 (FIG. 28)
and the proximal external thread 4404 (FIG. 28) and the number of
rotations that will be possible while both sets of threads are
engaged with the anchors (4100 and 4200) before the dual threaded
spanning distraction rod 4400 reaches the distal end of one or both
anchors. Dual threaded spanning distraction rods 4400 having a
particular thread pair ratio may be provided in a range of overall
lengths so that the distal external thread 4428 (FIG. 28) may
engage the distal anchor 4100 about the same time that the proximal
external thread 4404 (FIG. 28) engages the proximal anchor
4200.
A procedure that calls for the imposition of a relatively large
increase in the intervertebral disc height may use a dual threaded
spanning distraction rod with a large difference in thread pitches
in order to increase the potential to impose distraction. The
anchors will be selected to have the appropriate internal thread
pitches to work with the thread pitches on the on dual threaded
spanning distraction rod.
FIG. 30 shows assembly 5750 with distal anchor 5100 and proximal
anchor 5200. Note that the threaded bore 5112 of the distal anchor
5100 has a smaller diameter than does threaded bore 5216. Instead
of dual threaded spanning distraction rod 4400 and stabilization
rod 4600, assembly 5750 has only a dual threaded spanning
distraction rod 5700. As dual threaded spanning distraction rod
5700 does not have large ports 4420 (FIG. 28) there is not a need,
nor is there room for a stabilization rod.
Dual threaded spanning distraction rod 5700 has a driver engagement
section 5732, proximal external thread 5704 to engage the threaded
bore 5216 of the proximal anchor 5200, and a distal external thread
5728 to engage the threaded bore 5112 of the distal anchor 5100
after passing through the center of threaded bore 5216. The
imposition and reduction of distraction using the dual threaded
spanning distraction rod 5700 operates in the same manner as the
dual threaded spanning distraction rod 4400 (FIG. 29). The primary
difference being that dual threaded spanning distraction rod 4700
cannot be used to deliver material to the intervertebral disc
space. Thus, material must be delivered via trans-sacral access
before the addition of dual threaded spanning distraction rod 5700
(and possibly before the delivery of one or both anchors) or
material must be delivered by a non-trans-sacral access route.
Material Choices
While dual threaded spanning distraction rod 4700 may be fabricated
from a relatively rigid biocompatible material such as titanium,
other materials may be selected. A designer may opt to make all or
at least the portion of the dual threaded spanning distraction rod
between the threaded sections out of a material that is not as
stiff as titanium. The material chosen may be selected as having
mechanical properties that partially emulate the properties of
cancellous bone. One choice is PEEK (polyaryletheretherketone).
While Young's Modulus for cancellous bone is substantially less
than Young's Modulus for PEEK, the value for PEEK is much closer
than the Young's Modulus for titanium. Thus, PEEK is apt to behave
more like cancellous bone than is titanium. Young's Modulus values
for titanium alloys, PEEK, and cancellous bone are: 105-120 GPa,
3700 MPa, and 100 MPa.
The material chosen may actually have a Young's Modulus less than
cancellous bone, particularly if the material was used in a spring
or other structure to alter the effective mechanical
properties.
Alternatives, Options, and Variations
The driver engagement sections shown as hexagonal sockets could be
made in some other shape. The concave rounded segments of the hex
sockets could be made with another shape sufficient to orient a
driver and to preclude a driver not provided with that shape (or
with the full set of shapes needed to interact with two or more
special faces) from being inserted into the driver engagement
section.
The fluted pattern shown in FIG. 8 and FIG. 10 could be replaced
with some other pattern that reduces the surface contact between
the distal portion of the spanning distraction rod and the
component with which it engages. The pattern would not have to be
symmetrical.
While the examples given above used one external thread in each
threaded segment, those of skill in the art are aware that a rod
may be created with two or more helical threads. Nothing in this
disclosure precludes the use of two or more helical threads.
The dimensions and the proportions of the dimensions of the
components could be changed to accommodate the specific needs of
the surgery including modifications needed for the location in the
spine receiving therapy and the size of the vertebrae such as the
sizes found in an unusually large or small patient or in an animal
receiving spine therapy.
One of skill in the art will recognize that some of the alternative
implementations set forth above are not universally mutually
exclusive and that in some cases additional implementations can be
created that employ aspects of two or more of the variations
described above. Likewise, the present disclosure is not limited to
the specific examples or particular embodiments provided to promote
understanding of the various teachings of the present disclosure.
Moreover, the scope of the claims which follow covers the range of
variations, modifications, and substitutes for the components
described herein as would be known to those of skill in the
art.
To assist the reader and for the sake of completeness, several
applications or patents have been referenced. While these earlier
applications have been incorporated by reference to provide
additional detail it should be noted that these other applications
(including those that have subsequently issued as patents) were
written at an earlier time and had a different focus from the
present application. Thus, to the extent that the teachings or use
of terminology differ in any of these incorporated applications
from the present application, the present application controls.
The legal limitations of the scope of the claimed invention are set
forth in the claims that follow and extend to cover their legal
equivalents. Those unfamiliar with the legal tests for equivalency
should consult a person registered to practice before the patent
authority which granted this patent such as the United States
Patent and Trademark Office or its counterpart.
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